Pads and pin-outs in three dimensional integrated circuits

ABSTRACT

A three dimensional semiconductor device, comprising: a substrate including a plurality of circuits; a plurality of pads, each pad coupled to a circuit; and a memory array positioned above or below the substrate and coupled to a circuit to program the memory array.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of and claims priority to U.S. patentapplication Ser. No. 11/986,023, filed on Nov. 19, 2007, which is herebyincorporated by reference in its entirety.

This application is related to U.S. patent application Ser. No.10/267,484, filed on Oct. 8, 2002 (now abandoned), U.S. patentapplication Ser. No. 10/267,511, filed on Oct. 8, 2002 (now U.S. Pat.No. 6,747,478), U.S. patent application Ser. No. 10/267,483, filed onOct. 8, 2002 (now abandoned), U.S. patent application Ser. No.10/762,627, filed on Jan. 23, 2004 (now U.S. Pat. No. 7,018,875), U.S.patent application Ser. No. 10/413,809, filed on Apr. 14, 2003 (now U.S.Pat. No. 6,855,988), U.S. patent application Ser. No. 10/413,810, filedon Apr. 14, 2003 (now U.S. Pat. No. 6,828,689), and U.S. patentapplication Ser. No. 11/986,024, filed on Nov. 19, 2007 (now U.S. Pat.No. 7,812,458), which all are hereby incorporated by reference in theirentirety.

FIELD

Embodiments relate to pads & pin-outs for multi-dimensional integratedcircuits.

BACKGROUND

Integrated circuits (ICs) comprise complex circuit blocks, each circuitblock further comprising a plurality of transistors. The transistors arenormally constructed on a semiconductor substrate. Metal interconnectscouple transistors. Pad structures are formed within the IC to couplethe IC to external devices. A pad structure includes a metal pad tofacilitate bonding of the IC in a printed-circuit-board (PCB). Withinthe IC, the metal pad couples to one or more circuits, typically inputcircuits or output circuits, to facilitate coupling of the externaldevice to the IC. Thus a pad in a first IC couples to a pad in a secondIC. Pad structures occupy a significant silicon area as each padstructure includes a metal pad, input or output buffers,electro-static-discharge (ESD) circuits, control circuits, clockcircuits, registers, etc. Metal pads itself is very large to facilitatebonding. Thus the pad cost for a given plurality of ICs required in areference system design is significant. Furthermore as pads couplebetween IC's, the I/O characteristics are extremely important tointerface devices.

Traditionally, integrated circuit (IC) devices such as custom,semi-custom, or application specific integrated circuit (ASIC) deviceshave been used in electronic products to reduce cost, enhanceperformance or meet space constraints. However, the design andfabrication of custom or semi-custom ICs can be time consuming andexpensive. The customization involves a lengthy design cycle during theproduct definition phase and high Non Recurring Engineering (NRE) costsduring manufacturing phase. Further, should bugs exist in the custom orsemi-custom ICs, the design/fabrication cycle has to be repeated,further aggravating the time to market and engineering cost. As aresult, ASICs serve only specific applications and are custom built forhigh volume and low cost applications.

Another type of semi custom device called a Gate Array customizesmodular blocks at a reduced NRE cost by synthesizing the design using asoftware model similar to the ASIC. The missing silicon level designverification results in multiple spins and lengthy design iterations.

In recent years there has been a move away from custom or semi-customICs towards field programmable components whose function is determinednot when the integrated circuit is fabricated, but by an end user “inthe field” prior to use. Off the shelf, generic Programmable LogicDevice (PLD) or Field Programmable Gate Array (FPGA) products greatlysimplify the design cycle. These products offer user-friendly softwareto fit custom logic into the device through programmability, and thecapability to tweak and optimize designs to optimize siliconperformance. The flexibility of this programmability is expensive interms of silicon real estate, but reduces design cycle and upfront NREcost to the designer. Most FPGA solutions mandate an external memory(boot-ROM) to store configuration data, thus exacerbating the solutioncost. The FPGA to memory interface is via high silicon consuming padstructures.

FPGAs offer the advantages of low non-recurring engineering costs, fastturnaround (designs can be placed and routed on an FPGA in typically afew minutes), and low risk since designs can be easily amended late inthe product design cycle. It is only for high volume production runsthat there is a cost benefit in using the more traditional approaches.However, the conversion from an FPGA implementation to an ASICimplementation typically requires a complete redesign. Such redesign isundesirable in that the FPGA design effort is wasted. An ASIC does notrequire configuration data and does not interface with a boot-ROM.

Compared to PLD and FPGA, an ASIC has hard-wired logic connections,identified during the chip design phase, and need no configurationmemory cells. This is a large chip area and cost saving for the ASIC.Smaller ASIC die sizes lead to better performance. A full custom ASICalso has customized logic functions which take less gate counts comparedto PLD and FPGA configurations of the same functions. Thus, an ASIC issignificantly smaller, faster, cheaper and more reliable than anequivalent gate-count PLD or FPGA. The trade-off is betweentime-to-market (PLD and FPGA advantage) versus low cost and betterreliability (ASIC advantage).

There is no convenient migration path from a PLD or FPGA used as adesign verification and prototyping vehicle to the lower die size ASIC.All of the SRAM or Anti-fuse configuration bits and programmingcircuitry has no value to the ASIC. Programmable module removal from thePLD or FPGA and the ensuing layout and design customization is timeconsuming with severe timing variations from the original design. Thepad structures play a major role in FPGA I/O interface characteristics,and matching those in a design conversion is not a simple exercise.

FIG. 1A shows prior-art arrangement of a first IC 100 coupled to asecond IC 101. The first IC 100 includes a first transistor layer 102having one or more circuit blocks 104. IC 100 includes one or more metalpads 103, each pad coupled to a circuit block such as 104. Typically,metal pad 103 is located substantially above the transistor layer 102.When IC 100 is an FPGA, circuit blocks 104 include I/O blocks,programmable logic blocks, and configuration memory. Data at pad 103 isreceived by a first circuit block 104 interfacing the pad, and thenprogrammed into memory elements within configuration circuits. Second IC101 includes a second transistor layer 106 having one or more circuitblocks 108. Each metal pad 107 in IC 101 is coupled to a circuit blocksuch as 108. When IC 101 is a memory device, circuit blocks 108 includeI/O blocks, memory arrays, and sense amplifiers. Datareceived/transmitted at pad 107 is handled by a circuit block 108interfacing the pad. Thus pads 103 and 107 form a bus structure for datatransfer between devices. FIG. 1B shows a second embodiment of prior artdevice coupling. In FIG. 1B, pads 107 and 103 are first coupled to acommon metal trace 120. Both ICs incur a large Si area for I/O's, andhave limited pads to connect to each other.

SUMMARY

In one aspect, a pad system is provided for a three-dimensionalsemiconductor device includes a first module layer having a plurality ofcircuit blocks; and a second module layer positioned substantially abovethe fast module layer, including a plurality of configuration circuitsto control a portion of the circuit blocks.

In another aspect, a three dimensional semiconductor device comprises: asubstrate including a plurality of circuits; a plurality of pads, eachpad coupled to a said circuit; and a memory array positioned above orbelow the substrate coupled to a said circuit to program the memoryarray.

In yet another aspect, a semiconductor device includes a plurality ofpads; a first layer including a memory array; and a second layerincluding input/output circuits coupled to the pads and positioned aboveor below the first layer, the second layer including one or morecircuits coupled to the memory array to program the memory array.

Implementations of the above aspect may include one or more of thefollowing. The memory array includes a memory element coupled to one ormore programmable logic circuits on the second layer to configure theprogrammable logic circuits. The memory array comprises one of: randomaccess memory to form an FPGA, a metal mask to form an ASIC. The padsare coupled to a ball grid array. The pads are coupled to leads in apackage. The pads are positioned along a perimeter of a device. The padsare positioned on the top or bottom surface on a device. The pads have apredetermined position within the device. The second layer includes aninput buffer to receive data from the pad to configure the memory array.The memory array can include fuses, antifuses, SRAM cells, DRAM cells,metal optional links, EPROMs, EEFROMs, flash, resistance modulatingelements, magneto-electric elements, photo-electric elements andferro-electric elements. The memory array controls a plurality of logiccircuits positioned in a predetermined position. The area of the memoryarray substantially overlaps the area of one or more programmable logiccircuits. The area of the memory array substantially under-laps the areaof one or more programmable logic circuits. The memory array and thepads are positioned substantially above the programmable logic circuits.The memory array and the pads are positioned substantially below theprogrammable logic circuits. The second layer includes drivers to writedata to the memory array. The first layer comprises drivers to writedata to the memory array. The first layer can have sense amplifiers toread data from the memory array. The second layer can also have senseamplifiers to read data from the memory array. A driver circuit can beconnected to the memory array to configure the memory array. The memoryarray can include one or more memory elements each coupled to one ormore programmable logic elements to configure the programmable logicelement.

In yet another aspect, a method for fabricating a 3D device includesforming a first layer having a memory array; forming a second layerabove or below the first layer, the second layer including one or morecircuits coupled to the memory array to configure the memory array; andforming a plurality of pads, wherein one or more pads are coupled to thesecond layer to provide input/output for the 3D device to program thememory array.

Implementations of the method may include one or more of the following.The memory array can be replaced by a metal pattern to convert an FPGAto an ASIC. The memory array can be programmed with a driver on thefirst layer. One or more programmable logic elements can be configuredwith configuration data stored in the memory array. The process includesdepositing thin film transistors on the first layer. The process alsoincludes depositing the first layer above a substrate. The second layercan be deposited above a substrate.

Other implementations may include one or more of the following. Theconfiguration circuits can be memory elements. Each memory element canbe a transistor or a diode or a group of electronic devices. The memoryelements can be thin film devices such as thin film transistors (TFT) ordiodes. The memory element can be selected from the group consisting ofvolatile or non volatile memory elements. The memory element can also beselected from the group of fuses, antifuses, SRAM cells, DRAM cells,metal optional links, EPROMs, EEPROMs, flash, resistance modulatingelements, magneto-electric elements, photo-electric elements andferro-electric elements. One or more redundant memory cells can beprovided for controlling the same circuit block. A third module layercan be formed substantially above the first and second module layer,wherein interconnect and routing signals are formed to connect thecircuit blocks within the first and second module layers. The thirdmodule layer can be formed substantially below the first and secondmodule layer. Alternatively, third and fourth module layers, whereininterconnect and routing signals are formed can be positioned above andbelow the second module layer respectively. The circuit block cancontain a programmable logic block which responds to input data signalsand develops corresponding complete or partial output logic signals, andregisters to store the logic signals and either outputting them tooutput terminals or returning them as inputs to additional programmablelogic blocks. The programmable logic blocks can contain pass gate logic,multiplexer logic, truth table logic, or AND/OR logic blocks.

Implementations of the above aspect may further include one or more ofthe following. The memory can be implemented using a TFT processtechnology that contains one or more of replaceable Fuses, Anti-fusesand SRAM elements. The process implementation is possible with anyprocess technology where EPROM, EEPROM, Flash, Ferro-Electric or anyother programmable element is vertically integrated.

In a second aspect, a multidimensional semiconductor device includes afirst module layer having a plurality of circuit blocks formed on afirst plane; and a second module layer formed on a second plane,including a plurality of configuration circuits formed to control aportion of the circuit blocks.

In a third aspect, a system includes a processor; data storage devicescoupled to the processor; and a three-dimensional semiconductor devicecoupled to the processor, the 3D semiconductor device having a firstmodule layer having a plurality of circuit blocks formed on a firstplane and a second module layer formed on a second plane, including aplurality of configuration circuits formed to control a portion of thecircuit blocks.

In a fourth aspect, a multi-dimensional semiconductor device includes aplurality of circuit blocks formed on a substrate; and a plurality ofconfiguration circuits formed substantially above the substrate tocontrol at least one circuit block.

Implementation of the fourth aspect may include one or more of thefollowing. The configuration circuit includes a predetermined conductivepattern to control the circuit blocks. The configuration circuits can bememory elements with one device selected from the following: diode,transistor, thin film, device, thin film resistor, thin film capacitor,thin film transistor (TFT). The memory element can be selected from thegroup consisting of volatile or non volatile memory elements. The memoryelement can also be selected from a group of fuse links, antifusecapacitors, SRAM cells, DRAM cells, metal optional links, EPROM cells,EEPROM cells, flash cells, resistance modulating elements,magneto-electric elements, photo-electric elements and ferro-electricelements.

Implementations of the above aspects may include one or more of thefollowing. The IC product is re-programmable in its initial stage withturnkey conversion to an ASIC. The IC has the end ASIC cost structureand FPGA re-programmability. The IC product offering occurs in twophases: the first stage is a generic FPGA that has re-programmabilitycontaining a programmable module, and the second stage is an ASIC withthe entire programmable module replaced by 1 to 2 customized hard-wiremasks. There is no change to pads and circuits coupled to pads in thechange from FPGA to ASIC—thus no I/O characteristics are altered.Peripheral devices couple to FPGA and ASIC canonicals without changes ininterface properties.

A series product families can be provided with a modularizedprogrammable element in an FPGA version followed by a turnkey customASIC with the same base die with 1-2 custom masks. The verticallyintegrated programmable module does not consume valuable silicon realestate of a base die. Furthermore, the design and layout of theseproduct families adhere to removable module concept: ensuring thefunctionality and timing of the product in its FPGA and ASIC canonicals.These IC products can replace existing PLD and FPGA products and competewith existing Gate Arrays and ASIC's in cost and performance.

Advantages of the IC may include one or more of the following. An easyturnkey customization of an ASIC from an original smaller PLD or FPGAwould greatly enhance time to market, performance, low cost and betterreliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A & 1B show pads & pin-outs in prior art ICs.

FIG. 2A shows a cross sectional view of a first embodiment of a 3Dintegrated circuit.

FIG. 2B shows a cross sectional view of a second embodiment of a 3Dintegrated circuit.

FIG. 3A shows a cross sectional view of a first embodiment of a 3D FPGA.

FIG. 3B shows a cross sectional view of the first embodiment FPGAconverted to an ASIC.

FIG. 3C shows a 3D view of the FPGA and ASIC embodiments.

FIG. 4A shows a cross sectional view of a second embodiment of a 3DFPGA.

FIG. 4B shows a cross sectional view of the second embodiment FPGAconverted to an ASIC.

FIGS. 5A & 5B show cross sectional views of modularized 3D devices.

FIG. 6A shows an exemplary AND-OR PLD Architecture.

FIG. 6B shows an exemplary AND-OR array gate realization of PLD.

FIG. 7A shows one EEPROM implementation of a P-Term logic array.

FIG. 7B shows P-term configuration for SRAM/hard-wired PLD architecture.

FIG. 8A shows an exemplary pass-gate logic.

FIG. 8B shows an exemplary 4-Input logic MUX.

FIG. 8C shows an exemplary 2-Input Truth Table (Look-Up-Table).

FIG. 9 shows a logic tree implementation of a 4-Input Truth Table (LUT).

FIG. 10 shows an exemplary 6T SRAM.

FIG. 11 shows pass gate transistor logic controlled by SRAM.

FIG. 12 shows one embodiment of a 5×6 switch matrix.

FIG. 13 shows pass gate controlled by Vcc (power) or Vss (ground)

FIG. 14 shows the 5×6 switch matrix

DESCRIPTION

In the following detailed description of the invention, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown, by way of illustration, specific embodiments in which theinvention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention. Other embodiments may be utilized and structural, logical,and electrical changes may be made without departing from the scope ofthe present invention.

Definitions: The terms “wafer” and “substrate” used in the followingdescription include any structure having an exposed surface with whichto form the integrated circuit (IC) structure of the invention. The termsubstrate is understood to include semiconductor wafers. The termsubstrate is also used to refer to semiconductor structures duringprocessing, and may include other layers that have been fabricatedthereupon. Both wafer and substrate include doped and undopedsemiconductors, epitaxial semiconductor layers supported by a basesemiconductor or insulator, SOI material as well as other semiconductorstructures well known to one skilled in the art. The term “conductor” isunderstood to include semiconductors, and the term “insulator” isdefined to include any material that is less electrically conductivethan the materials referred to as conductors. Thus every IC includes asubstrate.

The term “module layer” includes a structure that is fabricated using aseries of predetermined process steps. The boundary of the structure isdefined by a first process step, one or more intermediate process steps,and a final process step. The resulting structure is formed on asubstrate. A cross-section of a semiconductor device may be used toidentify module layer boundaries. It is understood that some processingsteps such as resist patterning and cleans do not leave structuralimprints to a module layer. It is further understood that someprocessing steps such deposition and etching leave structural imprintsin a module layer. Thus a module layer includes processing steps thatmay or may not make a structural imprint.

The term “pass-gate” and “switch” refers to a structure that can pass asignal when on, and block signal passage when off. A pass-gate connectstwo points when on, and disconnects two points when off. A pass-gatecouples two points when on, and decouples two points when off. Apass-gate can be a floating-gate transistor, an NMOS transistor, a PMOStransistor or a CMOS transistor pair. The gate electrode of transistorsdetermines the slate of the connection. A CMOS pass-gate requirescomplementary signals coupled to NMOS and PMOS gate electrodes. Acontrol logic signal is connected to gate electrode of a transistor forprogrammable logic. A pass-gate can be a conductivity modulatingelement. The conductivity may be made to change between a sufficientlyconductive state and a sufficiently nonconductive state by aconfiguration means. The configurable element may comprise a chemical,magnetic, electrical, optical, and ferroelectric or any other propertythat allows the element to change its conductivity between said twostates.

The term “configuration circuit” includes one or more configurableelements and connections that can be programmed for controlling one ormore circuit blocks in accordance with a predetermined user-desiredfunctionality. The configuration circuit includes the memory element andthe access circuitry, herewith called memory circuitry, to modify saidmemory element. A memory element in the configuration circuit is coupledto a programmable circuit block to configure the circuit block. Thus aconfiguration circuit is different from traditional circuits in memorydevices. Configuration circuit does not include the logic pass-gatecontrolled by said memory element. In one embodiment, the configurationcircuit includes a plurality of memory elements to store instructions toconfigure an FPGA. In another embodiment, the configuration circuitincludes a first selectable configuration where a plurality of memoryelements is formed to store instructions to control one or more circuitblocks. The configuration circuit includes a second selectableconfiguration with a predetermined conductive pattern formed in lieu ofthe memory circuit to control substantially the same circuit blocks. Thememory circuit includes elements such as diode, transistor, resistor,capacitor, metal link, among others. The memory circuit also includesthin film elements. In yet another embodiment, the configuration circuitincludes a predetermined conductive pattern comprising one or more ofvia, resistor, capacitor or other suitable ROM circuits in lieu of RAMcircuits to control circuit blocks. Configuration circuit should not beconfused with memory circuits in memory devices.

The term “horizontal” as used in this application is defined as a planeparallel to the conventional plane or surface of a wafer or substrate,regardless of the orientation of the wafer or substrate. The term“vertical” refers to a direction perpendicular to the horizontaldirection as defined above. Prepositions, such as “on”, “side”,“higher”, “lower”, “over” and “under” are defined with respect to theconventional plane or surface being on the top surface of the wafer orsubstrate, regardless of the orientation of the wafer or substrate.

FIG. 2A shows a cross sectional view of a first embodiment of anintegrated circuit that can be select-ably fabricated as either an FPGAor an ASIC. In this embodiment, a three-dimensional semiconductor device200 is shown. The device 200 includes a first module layer 202 having aplurality of circuit blocks 204 embedded therein. Module 202 includestransistors. Module 202 may be constructed on a semiconductor substratelayer or thinned down semiconductor substrate layer comprising highmobility devices. Module 202 may be constructed on a SOI substratecomprising high mobility transistors. The first module layer may includeone or more metal layers. The device 200 also includes a second modulelayer 206 formed substantially above the first module layer 202. Thesecond module layer may be deposited or bonded or glued on to firstmodule layer. The second module layer 206 includes a plurality ofcircuit blocks 208 embedded therein. The second module layer may beconstructed on a second semiconductor substrate, thinned downsemiconductor layer or an SOI substrate. The second module may bepositioned above metal and require low temperature processing. Thesecond module layer transistors may have a lower mobility compared tothe first module layer transistors. The second module transistors may bethin-film transistors (TFT's). Circuit blocks 208 may include one ormore configuration circuits. Generic configuration circuits 208 areformed to store instructions to control a portion of the circuit blocks204. In the embodiment of FIG. 2A, wiring/routing interconnects (inmodule layers 202 and 206, not shown) are formed to couple circuitblocks 204, circuit blocks 208 and pads 207. One or more pads 207 maynot directly connect to circuit block 208. Thus no ESD structures or I/Obuffers (i.e. high current circuits) may be required in circuits 208,which allows transistor layer 206 to accommodate low mobilitytransistors. Lower mobility transistors offer greater flexibility overhigher mobility transistors to be fabricated within the second modulelayer 206. Furthermore, I/O Memory data received at pad 207 is firstreceived by circuit blocks 204 in first module layer 202, and thenwritten into configuration circuits 208, preserving high data interfaceas well as high circuit density. Circuits 208 may further couple tocircuits 204 in the full construction of the FPGA or ASIC.

FIG. 2B shows across sectional view of a second embodiment of anintegrated circuit that can be select-ably fabricated as either an FPGAor an ASIC. In this embodiment, a three-dimensional semiconductor device220 is shown. The device 220 includes a first module layer 212 having aplurality of circuit blocks 214 embedded therein. Module 212 includestransistors. Module 212 may be constructed on a semiconductor substratelayer or thinned down semiconductor substrate comprising high mobilitydevices. Module 212 may be constructed on a SOI substrate comprisinghigh mobility transistors. The first module layer may include one ormore metal layers. The first module layer may 212 be laser annealed toimprove the mobility of transistors. The device 220 also includes asecond module layer 216 formed substantially below the first modulelayer 212. The second module layer may be deposited or bonded or gluedon to first module layer. The second module layer 216 includes aplurality of circuit blocks 218 embedded therein. The second modulelayer may be constructed on a second semiconductor substrate, thinneddown semiconductor layer or an SOI substrate. The second module may bepositioned below or above metal and may require low temperatureprocessing. The second module layer transistors may have a lowermobility compared to the first module layer transistors. The secondmodule transistors may be thin-film transistors (TFT's). Circuit blocks218 may include one or more configuration circuits. In the embodiment ofFIG. 2B, wiring/routing interconnects (in module layers 212 and 216, notshown) are formed to couple circuit blocks 214, circuit blocks 218 andpads 213. One or more pads 213 may not directly connect to circuit block218. Thus no ESD structures or I/O buffers (i.e. high current circuits)may be required in circuits 218, which allows transistor layer 216 toaccommodate low mobility transistors. Lower mobility transistors offergreater flexibility over higher mobility transistors to be fabricatedwithin the second module layer 216. Furthermore, I/O Memory datareceived at pad 213 is first received by circuit blocks 214 in firstmodule layer 212, and then written into configuration circuits 218,preserving high data interlace as well as high circuit density. Circuits218 may further couple to circuits 214 in the full construction of theFPGA or ASIC.

FIGS. 3A and 3B show an FPGA conversion to an ASIC. FIG. 3A shows across-sectional view of the FPGA. In that, pads 307 interlaces withcircuits 304 in module layer 302. Module layer 302 may is a transistorlayer as it comprises transistors, the transistors forming one or morecircuit blocks 404 and one or more programmable circuit blocks 305. Inthe FPGA, module layer 306 comprises a second transistors fabricated ona thin-film layer positioned substantially above (or below, as in FIG.2B) the module layer 302. The configuration circuit includes a pluralityof memory elements to store configuration data. Each memory element iscoupled to one or more programmable logic elements within circuit blocks305, the memory data programming the logic elements and routing elementsto a user specification. Data stored in the configuration circuits canbe changed by the user, thus altering the programmable logicapplication. Memory data in configuration circuit 308 may beRandom-Access-Memory (RAM) such as SRAM, DRAM, NVRAM etc. Memory data inconfiguration circuit 308 may be Programmable Read-Only-Memory (ROM)such as EPROM, EEPROMR, Fuses, Anti-fuses etc. Such products offerchangeable memory content in the configuration circuit for a user toselect a desire memory pattern to program the FPGA. The FPGA issues acommand requesting configuration data from an external boot-ROM. Thedata stream for configuration memory may enter the device thru one ormore pads such as 307. A said pad 307 is coupled to circuit block 304 inthe module layer 302. The data may enter as a single-bit stream, or asan 8-bit (byte) stream or in any other standard data transfer format.The date may be routed by circuit blocks 304 in module layer 302 toconfiguration circuits 308 in module layer 306. The configuration datais stored within memory elements located in the configuration circuits308. Thus configuration data resides within the FPGA 200, in the secondmodule layer 306, to program the programmable logic content 305 inmodule layer 302 during normal operation of the FPGA. No pads arerequired to interface directly with configuration circuits in module 306to read or write memory data.

FIG. 3B shows a cross-sectional view of the device in FIG. 3A in ASICmode. The base die including transistor module layer 302 and pads 307are identical to the FPGA in FIG. 3A. Thus the pad interface circuits tothe FPGA & ASIC are identical, and all I/O characteristics are identicalbetween the two. A substitution of FPGA device by the ASIC device has noimpact on interface requirements with peripheral devices coupled toeither of the devices. In the ASIC in FIG. 3B, module layer 316 nowincludes a configuration circuit 318 comprising a metal pattern in lieuof the memory elements of 308 in the FPGA. A metal pattern can provideROM elements by simply having hard wired power or ground connectionsinstead of memory storage units. Thus every memory element in FPGAconfiguration circuit 308 having a data one is replaced by wireconnections to power in ASIC configuration circuit 318, and every memoryelement in FPGA configuration circuit 308 having a data zero is replacedby wire connections to ground in ASIC configuration circuit 318. A metalpattern 318 is simpler to construct, cheaper and more reliable comparedto complex memory elements embedded in circuits 308. Additionally, as noconfiguration data external to ASIC in FIG. 3B is required, the ASIC isadjusted to simply not request external configuration data, or ignore anincoming bit-stream of data. These changes are included in circuitblocks 304 from the very beginning in anticipation of the FPGA to ASICconversion.

FIG. 3C shows a 3-dimensional view of either the FPGA or the ASICconstructed by alterable memory module, wherein pads are invariant tothe change. In FIG. 3C, a semiconductor device, comprises: a pluralityof pads 307 having predetermined positions; a first layer including aplurality of circuit blocks (IO circuit blocks 304, programmable circuitblocks 305, and other circuit blocks) having predetermined positions, asaid circuit block (such as 304) coupled to a said pad 307; and a secondlayer (306 or 316) positioned above or below the first layer including amemory array (308 or 318) coupled to one or more of said circuit blocks305, wherein the second layer comprises a plurality of configurations(such as 306 to form an FPGA, and 316 to form an ASIC) without alteringthe predetermined positions of circuit blocks 304, 305 and pads 307.FIG. 3C does not show all the metal layers constructed between the firstlayer, the second layer and the pad layer. In a typical process, thereare 10 or more such metal layers. In the circuit blocks 305 & 304 thereare programmable logic circuits and the memory array 308 comprisesmemory elements, a said memory element coupled to a said programmablelogic circuit to configure the programmable logic circuit. As thecontrol signals are vertical (compared to signal paths that run inhorizontal wires) there is no physical impact to locations of circuits304, 305 and pads 307 if the memory 308 is altered to 318 within thememory plane. Thus in the 3D device, pads that are coupled to power orground supply voltages remain the same for either memory configurations.Furthermore a pad 307 coupled to an Input/Output (I/O) circuit block 304in the first layer has the same I/O and pad coupling no matter what thememory implementation is. Thus the I/O characteristic is invariant tomemory array configurations. It is easily seen that the memory arraycould include any one of fuses, antifuses, SRAM cells, DRAM cells, metaloptional links, EPROMs, EEPROMs, flash, resistance modulating elements,magneto-electric elements, photo-electric elements or ferro-electricelements.

FIGS. 4A and 4B show another embodiment of convertible FPGA and ASICdevices. In FIG. 4, the configuration layer (406 in FPGA FIG. 4A, and416 in ASIC FIG. 4B) is positioned below the circuits layer 402 andcoupled to the circuit layer 402. The operation and conversion of FPGAin FIG. 4A and ASIC in FIG. 4B are identical to the discussion relatedto FIG. 3 and not repeated. The devices shown in FIG. 4 may beconstructed as monolithic devices, or separate die elements attached toform a 3D device.

FIG. 5A and FIG. 5B show cross sectional views of FPGA in FIG. 4A andASIC in FIG. 4B when constructed as monolithic devices. In FIG. 5A FPGA,module layer 524 is positioned between module layer 502 comprisingcircuit blocks 504 and module layer 506 comprising circuit blocks 508.Module layer 524 may include one or more metal layers required to format least a portion of interconnects to construct the IC. Module layer524 may be positioned above module layer 506, or below module layer 502.In the embodiment shown, module layer 502 is constructed on a substratelayer 522, which acts to dissipate thermal energy during normaloperation of the device. Module layer 522 may include a heat sink, orcoupled to a heat sink to dissipate power. In FIG. 5B ASIC, the metalinterconnects in module layer 534 are identical to metal interconnectsin module layer 524 of the FPGA. This no interconnect related timingparameters change between the two devices, memory elements in circuitblocks 514 are changed to metal patterns to freeze a selected memorycontent from the FPGA configuration memory. The coupling of memory toconfigure logic remains identical, preserving identical-bit patterndesigns between the two designs. Similarly, the module layer 532 is alsoidentical to module layer 522, thereby eliminating thermal variationsbetween the two devices. Finally, the pads 507 and their locations inFIG. 5A are identical to pads 513 and their locations in FIG. 5B—hencethe package encapsulating the device is identical between the twodevices. The user encounters no pin-out change, no I/O characteristicchange, and no configuration data change in the conversion of 3D FPGAdevice to the 3D ASIC device.

Fabrication of the IC shown in FIG. 5A also follows a modularized deviceformation. Formation of module layers 522, 502, 524 includingtransistors in circuit blocks 504 and routing wires in module layer 524is by utilizing a standard logic process flow used in a standard ASICfabrication. For the FPGA of FIG. 5A, extra processing steps used formodule layer 506 circuit blocks 508 fabrication are inserted into thelogic flow after module layer 524 is constructed. This includesfabrication steps for memory elements embedded in the configurationcircuits. For the ASIC of FIG. 5A, simpler metal pattern processingsteps are substituted to construct module layer 506. A significantbenefit with this manufacturing scheme is that all the masks associatedwith module layers 522, 502 and 524 are identical for the FPGA versionas well as the ASIC version, saving considerable NRE costs associatedwith mask costs. Metal pads and pad masks are also identical between thetwo devices. A full disclosure of the vertical integration of the TFTmodule using extra masks and extra processing is in the incorporated byreference applications disclosed.

Fabrication of the IC shown in FIG. 5B also follows a modularized deviceformation. A first die element of the device is formed by constructingcircuits 518 in module 516 on a substrate layer 532. Then one or moremetal interconnects are formed within module layer 516. A second dieelement is formed on an SOI material. First circuits 514 are formed onthe SOI. Then one or more metal layers are formed in the module layer534 above transistors module layer 512. The second die element is turnedup-side-down such that module layer 534 is positioned below module layer512. The two die elements are either bonded or glued such that metalconnects metal within module layer 534. The back-side substrate insecond die module is polished (removed) to expose the insulator. Padsare formed and coupled to circuit blocks 514. It is understood thatcoupling of pads 513 to circuits 514 may utilize one or more metallayers in module 534. One familiar in the art may define manyalternative variations to couple a firs transistor module layer with asecond transistor module layer maintaining a single pad structure forboth module layers.

During the customization from FPGA to ASIC, the base die and the data inthose remaining mask layers do not change making the logisticsassociated with chip manufacture simple. Removal of the SRAM (or anyother memory) module provides a low cost standard logic process for thefinal ASIC construction with the added benefit of a smaller die size. Ina first embodiment, the design timing is unaffected by this migration aslateral metal routing and silicon transistors are untouched. In a secondembodiment the ASIC timing is deliberately made faster by reducing wireloading and resistances associated with metal traces. In a thirdembodiment the metal trace loading and resistance is reduced to obtain asignificant power reduction in the ASIC migration. In all cases,software verification and the original FPGA design methodology provide aguaranteed final ASIC solution to the user. A full disclosure of theASIC migration from the original FPGA is in the co-pending incorporatedby reference applications discussed above.

In yet another embodiment of a programmable multi-dimensionalsemiconductor device, a first module layer is fabricated having aplurality of circuit blocks formed on a first plane. The programmablemulti-dimensional semiconductor device also includes a second modulelayer formed on a second plane. A plurality of configuration circuits isthen formed to store instructions to control a portion of the circuitblocks.

Next, details of the circuit blocks 204, the configuration circuit 208,and the wiring and/or routing circuit 524 in FIGS. 2A & 5A respectivelyare detailed.

A variety of digital or analog circuits can be used in circuit blocks204. These circuit blocks include programmable logic blocks to allowuser customization of logic. In one embodiment, programmable logicblocks are provided to respond to input data signals. The programmablelogic blocks develop corresponding complete or partial output logicsignals. Registers are used to store the output logic signals and eitheroutputting them to output terminals or returning them as inputs toadditional programmable logic blocks. The registers themselves can beprogrammable, allowing those to be configured such as T flip-flops, JKflip-flops, or any other register. The logic blocks may contain noregisters, or the registers may be programmed to be by-passed tofacilitate combinational logic implementation. The programmable logicblock can be selected from one of a pass gate logic, a multiplexerlogic, a truth table logic, or an AND/OR logic. FIG. 6A shows anexemplary AND-OR PLD Architecture. AND and OR arrays 602 and 604 containuser configurable programmable elements. FIG. 6B shows an exemplaryAND-OR array gate realization of a three input, four P-term, four outputPLD. The AND and OR array 610-612 are shown programmed to a specificpattern.

In yet other embodiments, the circuit block 204 contains a RAM/ROM logicblock consisting of “logic element tree” or “P-Term logic array” blocksthat perform logic functions. FIG. 7A shows one such NAND EEPROMimplementation of a P-Term in NAND-NOR logic array, while FIG. 7B showsthe same P-term configuration for either SRAM, or hard-wired PLDarchitectures. FIG. 7A shows two mirrored outputs P1 and P2. For outputP1 an AND gate 732 receives signals from pass transistors 722, 724, 728and 730. The pass transistor 722 is controlled by block 720 shown in thedashed circle, while the pass transistor 728 is controlled by block 726shown inside the dashed circle. Similarly, the upper half of FIG. 7Bincludes an AND gate 752 that receives inputs from pass transistors 742,744, 748 and 750, respectively.

FIG. 8A shows exemplary pass-gate logic 810 connecting one input to oneoutput. The NMOS pass gate voltage level S0 determines an ON and OFFconnection. FIG. 8B shows exemplary 4-Input logic MUX implementing anoutput function O where O=I0*S0+I1*S1+I2*S2+I3*S3. In the MUX, only oneof S0 870, S1 872, S2 874, S3 876 has a logic one. The MUX isconstructed by combining four NMOS pass gate logic elements 820-826,each pass-gate as shown in FIG. 8A.

FIG. 8C shows exemplary 2-input truth table logic (or also known as2-input look-up-table logic) realization of an output function F where,F=/A*/B*S0+/A*B*S1+A*/B*S2+A*B*S3(/A means not A).The truth table logic (LUT) values are represented by S0, S1, S2 and S3.The realization is done through six inverters collectively designated840 and eight pass transistors collectively designated 830. Logic valuesare stored in 4 programmable registers. These programmable registers arecontained in the configuration circuits as part of configuration memory.

FIG. 9 shows a logic tree constructed with five 2-input truth tablelogic (LUT) blocks 920-928 to perform a full four input truth table. Afour input truth table has 16 possible logic values S0, S1, . . . S15.As the number of inputs grow to N, this logic tree construction requires2^(N) logic values, and 2^(N−1)) branches in the logic tree. For large Nvalues, a full truth table realization is less efficient compared to apartial product term AND-OR array realization.

In another embodiment, the programmable logic block can be aprogrammable microprocessor block. The microprocessor can be selectedfrom third party IP cores such as: 8051, Z80, 68000, MIPS, ARM, andPowerPC. These microprocessor architectures include Superscalar, FineGrain Multi-Threading (FGMT) and Simultaneous Multi-Threading (SMT) thatsupport Application Specific Packet Processing (ASPP) routines. Tohandle Programmable Network Interface (PNI) the processor can containhardware and software configurability. Hardware upgradeability can begreatly enhanced in microprocessors embedded in PLD's by making use ofthe available logic content of the PLD device. Programmable features caninclude varying processor speed, cache memory system and processorconfiguration, enhancing the degree of Instruction Level Parallelism(ILP), enhancing Thread level parallelism (TLP). Such enhancements allowthe user to optimize the core processor to their specific application.Cache parameters such as access latency, memory bandwidth, interleavingand partitioning are also programmable to further optimize processorperformance and minimize cache hit miss rates. Additionally, theprocessor block can be a Very Long Instruction Word (VLIW) processor tohandle multimedia applications. The processor block can include a cachecontroller to implement a large capacity cache as compared with aninternal cache.

While a PLD can be configured to do DSP functions, the programmablelogic block can also contain a digital signal processor (DSP), which isa special purpose processor designed to optimize performance for veryhigh speed digital signal processing encountered in wireless andfiber-optic networks. The DSP applications can include programmablecontent for cache partitioning, digital filters, image processing andspeech recognition blocks. These real-time DSP applications contain highinterrupt rates and intensive numeric computations best handled byhardware blocks. In addition, the applications tend to be intensive inmemory access operations, which may require the input and output oflarge quantities of data. The DSP cache memory may be configured to havea “Harvard” architecture with separate, independent program and datamemories so that the two memories may be accessed simultaneously. Thisarchitecture permits an instruction and an operand to be fetched frommemory in a single clock cycle. A modified Harvard architecture utilizesthe program memory for storing both instructions and operands to achievefull memory utilization. The program and data memories are ofteninterconnected with the core processor by separate program and databuses. When both instructions and operands (data) are stored in a singleprogram memory, conflicts may arise in fetching data with the nextinstruction. Such conflicts have been resolved in prior art for DSP's byproviding an instruction cache to store conflicting instructions forsubsequent program execution.

In yet another embodiment, programmable logic block can contain softwareProgrammability. These software functions are executed in DSP, ARM, orMIPS type inserted IP cores, or an external host CPU. Acceleratorsconnected by a configurable SRAM switching matrix enhance thecomputation power of the processors. The microprocessor has localpermanent SRAM memory to swap, read, and write data. The switch matrixis pre-designed to offer both hard-wire and programmable options in thefinal ASIC. In this situation, the circuit block 104 can be a functionalblock that performs well-defined, commonly-needed function, such asspecial D/A or A/D converter, standard bus interface, or such block thatimplements special algorithms such as MPEG decode. The specialalgorithms implemented can be hardware versions of software. Forexample, algorithms relating to digital radio or cellular telephone suchas WCDMA signal processing can be implemented by the functional block.Other functional blocks include PCI, mini-PCI, USB, UART blocks that canbe configured by specifying the SRAM logic blocks.

In yet another embodiment, the circuit block 204 can be memory such as aregister file, cache memory, static memory, or dynamic memory. Aregister file is an array of latches that operate at high speed. Thisregister length counter may be programmable by the user. A cache memoryhas a high access throughput, short access latency and a smallercapacity as compared with main memory. The cache memory may beprogrammable to partition between the different requirements of thesystem design. One such need is the division between L1 and L2 cacherequirements for networking applications. The memory can also be staticrandom access memory or (SRAM) device with an array of single port, ormulti-port addressable memory cells. Each cell includes a fourtransistor flip-flop and access transistors that are coupled toinput/output nodes of the flip-flop. Data is written to the memory cellby applying a high or low logic level to one of the input/output nodesof the flip-flop through one of the access transistors. When the logiclevel is removed from the access transistor, the flip-flop retains thislogic level at the input/output node. Data is read out from theflip-flop by turning on the access transistor. The memory can also bedynamic random access memory (DRAM). Generally, a DRAM cell consists ofone transistor and a capacitor. A word line turns on/off the transistorat the time of reading/writing data stored in the capacitor, and the bitline is a data input/output path. DRAM data is destroyed during read,and refresh circuitry is used to continually refresh the data. Due tothe low component count per bit, a high density memory device isachieved.

In another embodiment, the circuit block 204 can be an intellectualproperty (“IP”) core which is reusable for licensing from othercompanies or which is taken from the same/previous design. In core-baseddesign, individual cores may be developed and verified independently asstand-alone modules, particularly when IP core is licensed from externaldesign source. These functions are provided to the user as IP blocks asspecial hardware blocks or pre-configured programmable logic blocks. TheIP blocks connect via a programmable switching matrix to each other andother programmable logic. The hardware logic block insertion to anyposition in a logic sequence is done through the configurable logicmatrix. These hardware logic blocks offer a significant gate countreduction on high gate count frequently used logic functions, and theuser does not require generic “logic element” customization. In bothcases, the user saves simulation time, minimize logic gate count,improve performance, reduce power consumption and reduce product costwith pre-defined IP blocks. The switch matrix is replaced by hard-wiresin the final ASIC.

The circuit blocks 204 can also be an array of programmable analogblocks. In one embodiment, the analog blocks include programmable PLL,DLL, ADC and DAC. In another embodiment, each block contains anoperational amplifier, multiple programmable capacitors, and switchingarrangements for connecting the capacitors in such as a way as toperform the desired function. Switched capacitor filters can also beused to achieve an accurate filter specification through a ratio ofcapacitors and an accurate control of the frequency of a sampling clock.Multiple PLL's can be programmed to run at different frequencies on thesame chip to facilitate SoC applications requiring more than one clockfrequency.

The circuit blocks 204 also contain data fetch and data write circuitryrequired to configure the configuration circuits 208. This operation maybe executed by a host CPU residing in the system, or the PLD deviceitself. During power up, these circuits initialize and read theconfiguration data from an outside source, either in serial mode or inparallel mode. The data is stored in a predefined word length locallyand written to the configurability allocation. The programmedconfiguration data is verified against the locally stored data and aprogramming error flag is generated if there is a mismatch. Thesecircuits are redundant in the conversion of the PLD to an ASIC. However,these circuits are used in both FPGA and ASIC for test purposes, and hasno cost penalty. A pin-out option has a “disable” feature to disconnectthem for the customer use in the FPGA and ASIC.

Configuration circuits 208 provide active circuit control over digitalcircuits 204. One embodiment of the configuration circuit includes anarray of memory elements. The user configuration of this memory amountsto a specific bitmap of the programmable memory in a softwarerepresentation.

Suitable memory elements include volatile or non volatile memoryelements. In non-volatile memory (NVM) based products, configurable datais held in one of metal link fuse, anti-fuse, EPROM, Flash, EEPROMmemory element, or ferro-electric elements, resistance modulatingelements, photo-electric elements, magneto-electric elements or anyother property altering element. Some memory elements are one timeprogrammable (OTP), while others can be programmed multiple times. AnEPROM requires UV fight to erase data. Flash & EEPROM's lend toin-system programmability (ISP). In volatile products, the configurabledata storage can be SRAM cells or DRAM cells. With DRAM cells, the datarequires constant refresh to prevent losses from leakages. Additionally,one or more redundant memory cells controlling the same circuit blockcan be used to enhance device yield.

The components of the memory element array can be a resistor, capacitor,transistor or a diode. In another embodiment of the configurationcircuit, a memory element can be formed using thin film deposition. Thememory element can be a thin film resistor, thin film capacitor, thinfilm transistor (TFT) or a thin film diode or a group of thin filmdevices connected to form an SRAM cell.

This discussion is mostly on SRAM elements and can easily extend toinclude all other programmable elements. In all cases, the design needsto adhere to rules that allow programmable module elimination, with nochanges to the base die, a concept not used in PLD, FPGA, Gate Array andASIC products today.

An exemplary 6T SRAM cell, shown in FIG. 10, needs no high voltagecapability, nor added process complexity. The cell of FIG. 10 has twoback-to-back inverters 1050-1052 whose access is controlled by passtransistors 1054-1056. In addition, R-load & Thin Film Transistor (TFT)load PMOS based SRAM cells can be used for PLDs and FPGAs. To achievezero stand-by power by eliminating sensing circuitry, and reduce memoryelement count for low input functions, these SRAM cells are embedded intruth table logic (also called Look-Up-Table) based architectures.

Pass gate transistor logic 1160 controlled by SRAM is shown in FIG. 11.In this embodiment, the memory cell (such as the cell of FIG. 10) drivesthe pass transistor 1160 to affect an outcome. A 5×6-switch point matrix1270 controlled by 30-SRAM cells coupled to 30-NMOS pass gates is shownin FIG. 12. FIG. 13 shows the NMOS pass gate 1360 logic controlled bythe SRAM in FIG. 11 converted to hard-wire logic. A contact 1362,connected to Vcc (logic 1) or Vss (logic 0) depending on the SRAM logiccontent, replace the SRAM cell. The SRAM logic mapping to hard wireconnections are automatic and done by a software program that isverifiable against the bit-map.

Similarly, FIG. 14 shows the 5×6-switch point matrix 1470 hard-wired byreplacing the SRAM bits that control NMOS gates with hard-wires to Vccor Vss. In FIG. 14, the bubble may represent either SRAM or hard-wireVcc or Vss control on NMOS pass gates. In the case of Fuse or Antifusearrays, contact or no contact between the two metal lines in FIG. 11 or13 directly replaces the programmable element and there is no NMOSpass-gate needed.

The P-Term logic builds the core of PLD's and complex PLD's (CPLD's)that use AND-OR blocks 202-204 (or equivalent NAND-NOR type logicfunctions) as shown in the block diagram of FIG. 5 and one expansion isshown in FIG. 6B with AND gates 610 and OR gates 612. Gateimplementation of two inputs (I1, I2) and two P-terms (P1, P2) NANDfunction can be single poly EEPROM bits as shown in FIG. 6B. The dottedcircle contains the charge trapping floating gate, the programmingselect transistor, tunneling diode, a control gate capacitor andprogramming access nodes. The SRAM cell replaces that entire circle inthis invention as detailed next. The SRAM NAND-NOR array (also AND-ORarray) replacement has not been realized in prior art as SRAM cellsrequire Nwell & Pwell regions that consume large silicon area to preventlatch-up. The SRAM in TFT do not have well related constraints as NMOSand PMOS bodies are isolated from each other. Keeping the two pass gatesin silicon layers and moving SRAM to TFT layers allow P-Term logicimplementation with SRAM cells and subsequent replacement withhard-wires. In TFT SRAM conversion to final ASIC, the bubble on NMOSgate becomes a hard-wire connection to Vcc or Vss.

The length of input and output wires, and the drive on NMOS pass gatesand logic gate delays determine the overall PLD delay timing,independent of the SRAM cell parameters. By moving SRAM cell to TFTupper layers, the chip X,Y dimensions are reduced over 20% to 50%compared to traditional SRAM FPGA's, providing a faster logic evaluationtime. In addition, removal of SRAM cell later does not alter lateralwire length, wire loading and NMOS pass gate characteristic. Thevertical dimension change in eliminating the memory module is negligiblecompared to the lateral dimension of the ASIC, and has no impact ontiming. This allows maintaining identical timing between the FPGA andASIC implementations with and without the SRAM cells. The final ASICwith smaller die size and no SRAM elements have superior reliability,similar to an ASIC, leading to lower board level burn-in and fieldfailures compared to PLD's and FPGA's in use today.

Next, the wiring and/or routing circuit 522 in FIG. 5A is discussed. Thewiring and/or routing circuit connects each logic block to each otherlogic block. The wiring/routing circuit allows a high degree of routingflexibility per silicon area consumed and uniformly fast propagation ofsignals, including high-fanout signals, throughout the device. Thewiring module may contain one or more levels of metal interconnect.

One embodiment of a switch matrix is a 6×5 programmable switch-matrixwith 30 SRAM bits (or 30 Anti-fuses, or 30 fuses), shown in FIG. 12. Thebox in FIG. 12 contains the SRAM cell shown inside dotted box of FIG.11, where the pass gate makes the connection between the two wires, andthe SRAM bit holds the configuration data. In this configuration, thewire connection in circuit layer 212 occurs via a pass transistorlocated in circuit 214 controlled by an SRAM cell in circuit 218. Duringpower-up, a permanent non-volatile memory block located in the system,loads the correct configuration data into SRAM cells. In Fuse orAnti-fuse applications, the box simply represents the programmableelement in circuit 218 between the two wires in circuit layer 212.During the ASIC conversion this link is replaced with an open or shortbetween the wires.

Another embodiment provides short interconnect segments that could bejoined to each other and to input and output terminals of the logicblocks at programmable interconnection points. In another embodiment,direct connections to adjacent logic blocks can be used to increasespeed. For global signals that traverse long distances, longer lines areused. Segmented interconnect structures with routing lines of variedlengths can be used. In yet other embodiments, a hierarchicalinterconnect structure provides lines of short lengths connectable atboundaries to lines of longer lengths extending between the boundaries,and larger boundaries with lines of even longer length extending betweenthose boundaries. The routing circuit can connect adjacent logic blocksin two different hierarchical blocks differently than adjacent logicblocks in the same hierarchical block. Alternatively, a tile-basedinterconnect structure can be used where lines of varying lengths inwhich each tile in a rectangular array may be identical to each othertile. In yet another implementation, the interconnect lines can beseparated from the logic block inputs by way of a routing matrix, whichgives each interconnect line more flexible access to the logic blockinputs. In another embodiment, interconnect routing is driven byprogrammable buffers. Long wire lengths can be sub-divided into smallerlength segments with smaller buffers to achieve a net reduction in theoverall wire delay, and to obtain predictable timing in the logicrouting of the PLD.

Next, a brief description of the manufacturing process is discussed.During one embodiment of manufacturing, one or more digital circuits canbe formed on a substrate. Next, the process selectively fabricateseither a memory circuit or a conductive pattern substantially above thedigital circuits to control portion of digital circuits. Finally, theprocess fabricates interconnects and routing wires substantially abovethe digital circuits and memory circuits to connect digital circuits andone of the memory circuit or the conductive pattern. In anotherembodiment of manufacturing, one or more digital circuits can be formedon a substrate. Next, the process fabricates interconnects and routingwires substantially above the digital circuits, further providingconnection points for configuration circuits to couple into digitalcircuits. Then, the process selectively fabricates either a memorycircuit or a conductive pattern substantially above interconnects tocontrol a portion of digital circuits. Either the memory or theconductive pattern programs the FPGA or the ASIC respectively.

The process can be modified to fabricate a generic field programmablegate array (FPGA) with the constructed memory circuit or an applicationspecific integrated circuit (ASIC) with the constructed conductivepattern. Multiple ASICs can be fabricated with different variations ofconductive patterns. The memory circuit and the conductive pattern haveone or more substantially matching circuit characteristics. In thiscase, timing characteristics substantially unchanged by the circuitcontrol option. The process thus fabricates a programmable logic deviceby constructing digital circuits on a substrate; and constructing anon-planar circuit on the substrate after constructing the digitalcircuits, the non-planar circuit being either a memory deposited tostore data to configure the digital circuits to form a fieldprogrammable gate array (FPGA) or a conductive pattern deposited tohard-wire the digital circuits to form an application specificintegrated circuit (ASIC), wherein the deposited memory and theconductive pattern have substantially matching timing characteristics.In another embodiment, the hard-wire ASIC option may be incorporatedinto the digital circuit layer 102. In another embodiment, the hard-wireASIC option is incorporated into the routing layer 110.

Although an illustrative embodiment of the present invention, andvarious modifications thereof, have been described in detail herein withreference to the accompanying drawings, it is to be understood that theinvention is not limited to this precise embodiment and the describedmodifications, and that various changes and further modifications may beeffected therein by one skilled in the art without departing from thescope or spirit of the invention as defined in the appended claims.

What is claimed is:
 1. A semiconductor device, comprising: a first layerincluding a circuit; a second layer including a plurality of circuits ina first plurality of locations; a third layer including a plurality ofpads in a second plurality of locations, wherein the plurality of padsare inaccessible from the first layer; and a plurality of wireinterconnects that are positioned through a first portion of the thirdlayer and through a second portion of the second layer, wherein thecircuit is configured to depend on the second layer to operate, whereinthe first plurality of locations and the second plurality of locationsare configured to be independent of the first layer, and wherein thefirst layer, the second layer, and the third layer form a stack.
 2. Thesemiconductor device of claim 1, wherein the circuit is configured toprovide field-programmable gate array (FPGA) functionality.
 3. Thesemiconductor device of claim 2, wherein the circuit comprises a memoryelement for the FPGA functionality.
 4. The semiconductor device of claim1, wherein the first layer excludes pads.
 5. The semiconductor device ofclaim 1, wherein the circuit is configured to provideapplication-specific integrated circuit (ASIC) functionality.
 6. Thesemiconductor device of claim 5, wherein the circuit comprises amask-programmable metal pattern for the ASIC functionality.
 7. Thesemiconductor device of claim 1, wherein the plurality of circuitscomprise a plurality of programmable logic circuits.
 8. A method,comprising: forming a stack comprising a first layer including acircuit, a second layer including a plurality of circuits in a firstplurality of locations, a third layer including a plurality of pads in asecond plurality of locations, and a plurality of wire interconnectsthat are positioned through a first portion of the third layer andthrough a second portion of the second layer, wherein the plurality ofpads are inaccessible from the first layer; and coupling a portion ofthe plurality of circuits to the plurality of pads, wherein the circuitis configured to depend on the second layer to operate, and wherein thefirst plurality of locations and the second plurality of locations areconfigured to be independent of the first layer.
 9. The method of claim8, wherein the circuit is configured to provide field-programmable gatearray (FPGA) functionality.
 10. The method of claim 9, wherein thecircuit comprises a memory element for the FPGA functionality.
 11. Themethod of claim 8, wherein the first layer excludes pads.
 12. The methodof claim 8, wherein the circuit is configured to provideapplication-specific integrated circuit (ASIC) functionality.
 13. Themethod of claim 12, wherein the circuit comprises a mask-programmablemetal pattern for the ASIC functionality.
 14. The method of claim 8,wherein the plurality of circuits comprise a plurality of programmablelogic circuits.
 15. A semiconductor device, comprising: a substrateincluding a plurality of circuits in a first plurality of locations; afirst layer including a circuit; a second layer including a plurality ofpads in a second plurality of locations, wherein the plurality of padsare inaccessible from the first layer; and a plurality of wireinterconnects that are positioned through a first portion of the secondlayer and through a second portion of the substrate, wherein the circuitis configured to depend on the substrate to operate, wherein the firstplurality of locations and the second plurality of locations areconfigured to be independent of the first layer, and wherein thesubstrate, the first layer, and the second layer form a stack.
 16. Thesemiconductor device of claim 15, wherein the circuit is configured toprovide field-programmable gate array (FPGA) functionality.
 17. Thesemiconductor device of claim 16, wherein the circuit comprises a memoryelement for the FPGA functionality.
 18. The semiconductor device ofclaim 15, wherein the circuit is configured to provideapplication-specific integrated circuit (ASIC) functionality.
 19. Thesemiconductor device of claim 18, wherein the circuit comprises amask-programmable metal pattern for the ASIC functionality.
 20. Thesemiconductor device of claim 15, wherein the plurality of circuitscomprise a plurality of programmable logic circuits, and wherein thefirst layer excludes pads.